Active matrix backplane formed using thin film optocouplers

ABSTRACT

A device includes a backplane having multiple output terminals arranged in an array on an output surface of the backplane. The device further includes an active matrix array comprising thin film solid state optical switches coupled respectively between an input terminal of the backplane and the output terminals. Storage capacitors may be coupled respectively to the output terminals. A pixelated light source provides pixelated light that controls the optical switches.

TECHNICAL FIELD

This disclosure relates generally to active matrix arrays and to devicesand methods related to such arrays.

BACKGROUND

Active matrix arrays provide a way to access a large number ofelectronic elements. These arrays have typically been used to addresshigh density light emitting elements such as a liquid crystal display(LCD) or an organic light emitting diode (OLED) display. The activematrix array backplanes used to access the LCD or OLED display elementhave been made thin to facilitate flat panel displays. Active matrixaddressing can also be useful to control electronic elements that areactuated by high voltages. High voltage applications often involve theuse of some type of electrical isolation between control and outputcircuits. There is a need for high density active matrix arrays that areuseful for high voltage applications.

SUMMARY

Some embodiments involve a device that includes a backplane havingmultiple output terminals arranged in an array on an output surface ofthe backplane. The device includes an active matrix array comprisingthin film solid state optical switches coupled respectively between aninput terminal of the backplane and the output terminals. Storagecapacitors may be coupled respectively to the output terminals. Apixelated light source provides pixelated light that controls theoptical switches.

Some embodiments relate to a backplane that includes multiple outputterminals arranged on an output surface of the backplane and an activematrix array comprising thin film solid state optical switches coupledrespectively between at least one input terminal of the backplane andthe output terminals which are arranged in an array. Each optical switchincludes a layer of photo sensitive material that extends laterally;first and second electrodes spaced apart laterally from one anotheralong the layer of photo sensitive material, the first and secondelectrodes contacting the photo sensitive material at first and secondjunctions, respectively; and at least one field plate electricallyinsulated from the photo sensitive material and extending laterallyalong the layer of photo sensitive material and beyond the first andsecond junctions, wherein the at least one field plate is electricallyconnected to the first electrode or the second electrode.

These and other features and aspects of various embodiments may beunderstood in view of the following detailed discussion and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The discussion below makes reference to the following figures, whereinthe same reference number may be used to identify the similar/samecomponent in multiple figures.

FIG. 1 is a block diagram of a system that uses a optocoupler activematrix (optocam) backplane in accordance embodiments discussed herein;

FIG. 2 is a circuit diagram of an optocam backplane in accordance withsome embodiments;

FIG. 3 illustrates an exemplary input waveform for the optocam backplaneof FIG. 2;

FIG. 4 is a circuit diagram of an optocam backplane that uses two setsof input lines and two optical switches per pixel in accordance withsome embodiments;

FIGS. 5A1 and 5A2 is a circuit diagram of an optocam backplane thatincludes a digital to analog converter in each pixel in accordance withsome embodiments;

FIG. 5B illustrates a digital input waveform for the optocam backplaneof FIG. 5A;

FIG. 6 is a circuit diagram of an optocam backplane that includesmultiple color filters according to some embodiments;

FIG. 7 is a side view of an optocam backplane using a flat panel displayas the control light source in accordance with some embodiments;

FIG. 8 is a side view of an optocam backplane using a flat panel displayas the control light source and including optical elements disposedbetween the optocam backplane and the flat panel display in accordancewith some embodiments;

FIG. 9 illustrates an optocam backplane and a projector used as thecontrol light source in accordance with some embodiments;

FIGS. 10 and 11 are measured waveforms of an optocam backplane inaccordance with some embodiments;

FIG. 12 shows graphs of the dark and light current for a standard PINphotosensor;

FIGS. 13A and 13B show cross sectional and top views of a thin filmoptical switch in accordance with some embodiments;

FIG. 14 is a top view of a thin film optical switch that includes twofield plates according to some embodiments;

FIG. 15 provides dark and light IV characteristics for the opticalswitch illustrated in FIGS. 13A and 13B;

FIGS. 16A and 16B show cross sectional and top views of an opticalswitch having a p+/i/p+ structure in accordance with some embodiments;and

FIG. 17 provides dark and light IV characteristics for the opticalswitch illustrated in FIGS. 16A and 16B.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

Embodiments disclosed herein are directed to high density backplanesthat provide optocoupled, high voltage outputs. Optocoupling serves toisolate the high voltage nodes from the low voltage control system.Large area optocoupled backplanes are capable of providing arrays ofhigh voltage outputs and present opportunities for wide variety ofapplications including driving microelectromechanical (MEMS) devicessuch as membrane displays and optical mirror arrays. Some embodimentsdiscussed are directed to optocoupler active matrix (optocam)backplanes, that can include a large number of pixels, e.g., 500×500,1000×1000, or more, with an array pitch of less than about 100 μm. Invarious embodiments, the optical switches of the optocam backplane canbe controlled by pixelated light generated a flat panel display or aprojector. Some embodiments discussed herein involve novel thin filmoptical switches that can be used to provide the optocoupling for theoptocam backplane.

FIG. 1 is a cross sectional view of an exemplary system thatincorporates an optocam backplane 110 in accordance with variousembodiments discussed herein. The optocam backplane 110 has an outputsurface 130 that includes an array, e.g., a multi-dimensional array, atwo dimensional, or xy array, of output terminals 131. The outputterminals 131 can be coupled to drive a device 190, e.g., a MEMs array,etc.

Within the backplane 110, but not shown in FIG. 1, are thin film opticalswitches that couple an input voltage, e.g., a high voltage input, tothe output terminals 130. Structures of thin film optical switches thatcan provide high voltage outputs and which are suitable for the optocambackplane are discussed in more detail below. The optical switches ofthe backplane 110 are controlled by light source 120 that generatespixelated light 199 to activate the optical switches of the backplane110.

FIG. 2 is a schematic diagram of an optocam backplane 200 showing anumber of pixels 210 arranged in a two dimensional array. Each pixel 210includes an optical switch, e.g., optical switches 220, that can beturned on or off by the presence or absence of light 260. When opticalswitch 220 is turned on, input 250, e.g., a high voltage input, iscoupled to the pixel output terminal 230 through a low impedance andwhen the optical switch 220 is turned off, input 250 is decoupled fromthe pixel output terminal 230 by a high impedance between the input 250and output terminal 230. Each pixel can include an output storagecapacitor 240 coupled to the pixel output terminal 230. Instead of eachcolumn of pixels 210 being individually addressable, as is typical forrow scanning active matrix switched LCD display backplanes, the input(“data”) lines 250 of some or all the pixels 210 can be connected,providing a simplified 2 port electrical interface. Individual pixeladdressing is accomplished by the on/off control of individual pixels ofthe pixelated light generated by a light source (not shown in FIG. 2)that is optically coupled to the optical switches 220. Although FIG. 2shows an array of 4×4 pixels, the backplane 200 is scalable to 1K×1Kpixels or more.

In some embodiments, the each pixel 210 of backplane 200 has thecapability of providing multiple voltage levels at the output terminal230. The control light source does not need to produce multiple greylevels in order to achieve multi-level high voltage outputs on theoutput terminals 230 of the output terminal array. FIG. 3 shows anexemplary waveform 310 of the input line 250 driving voltage andportions of the waveform that provide the turn on timing 321, 322, 323for groups A, B, C of pixels. In this particular example, V1 will bestored in the storage capacitor of pixel group A, 0 will be stored inthe storage capacitor for pixel group B and V2 will be stored in thestorage capacitor for pixel group C. V1 and V2 can have oppositepolarity as illustrated or may have the same polarity as needed by theapplication. Any number of output voltage levels can be provided by thisprocess, with more grey levels being possible at the expense of areduced refresh rate.

FIG. 4 shows a schematic of an optocam backplane that providesmulti-level output voltages. The optocam backplane of FIG. 3 includesmultiple input lines 451, 452 and multiple optical switches 421, 422 inone pixel 410 to achieve multiple voltage levels. Each pixel 410 caninclude a storage capacitor 440 coupled to the optical switches 421,422, and to the output terminal 430. By modulating the light controllingthe optical switches 421, 422 in a pulse width modulation manner, theoutput voltage at the top output terminal 430 can be tuned to any levelbetween V1 and V2.

Alternatively, some two dimensional (2D) light sources, such as OLED orLCD displays, are capable of generating grey level light outputs foreach individual pixel. In embodiments which incorporate these types oflight sources, any voltage between V1 and V2 can be generated by therelative light level of light source that control optical switches 421and 422.

According to some implementations, V1 and V2 do not need to be DC orquasi-DC (no change during one of the light-source-on cycles). Instead,one or both of V1 and V2 can be driven by a high frequency voltagegenerator. In one example, V1 can be connected to a 1 MHz sinusoidalfunction generator and V2 can be connected to ground. Pixel groups withthe light source pixel that energizes optical switch 421 turned on willoutput 1 MHz voltage on the top electrode, while the pixel groups withthe light source pixel turned on that energizes optical switch 422 willoutput 0V. This configuration can enable devices or applications thatrequire high frequency drive. For example, if the optocam backplane isused for an arbitrary micro-particle actuator, this approach enablesdielectrophoretic actuation. The simpler optocam backplane shown in FIG.2 is also capable of selectively outputting high frequency potentials tothe top electrode. However, it does not provide selective “ground”electrodes, but rather, any backplane pixels not addressed withillumination will be connected to ground through the storage capacitor.For many applications, this should be sufficient.

FIGS. 5A (5A1 and 5A2) and 5B illustrate yet another embodiment ofgenerating multi-level high voltage outputs with only on/off control ofindividual light source pixels of the light source. Each pixel 510 ofthe optocam backplane includes a mini digital to analog converter (DAC)with an optical digital input. For example, FIG. 5A shows a backplanepixel configuration that has 3 bit digital input, each one controlled byan optical switch 521, 522, 523, and connected to a weighted capacitor581, 582, 583. Storage capacitor 540 is electrically connected to thebackplane pixel output terminal 530 and to each of the weightedcapacitors 581, 582, 583. Optical switches 521, 522, 523 are turned onin a pattern that coordinates with the input voltage waveform. FIG. 5Bshows the input waveform 570 applied to input terminal 571 of FIG. 5A.In the example shown in FIGS. 5A and 5B, optical switches 523 and 521are turned on during time interval 582 when the input voltage waveform570 is V1 and optical switch 522 is turned on during time interval 581when input voltage waveform is 0. Using the timing pattern 581, 582 andinput waveform 570 shown in FIG. 5B, the voltage at the output terminal530 of pixel 510 is (5/7)*V1. The reader will appreciate that variousother analog voltage levels may be achieved at the output terminal 530depending on the timing pattern and input voltage waveform used.

FIG. 6 is a schematic diagram of an optocam backplane having aconfiguration that can be used instead of doubling the resolutionrequirement of the light source. In this embodiment, the light source isa 2D color light source such as a color display. Each pixel 610 includestwo optical switches 621, 622. Color filter 671 is disposed betweenoptical switch 621 and the light pixel that energizes the optical switch621. Color filter 672 is disposed between optical switch 622 and thelight pixel that energizes the optical switch 622, wherein the opticalpassband of color filter 671 is different from the optical passband ofcolor filter 672. When light 681 of wavelengths within the passband ofcolor filter 671 is directed towards the backplane pixel 610, opticalswitch 621 is on and optical switch 622 is off. Conversely, when light682 having wavelengths within the passband of color filter 672 isdirected towards the backplane pixel 610, optical switch 622 is on andoptical switch 621 is off. Thus, it is possible to use a color displayto separately control each optical switch 621, 622 of the pixel 610. Thecolor display is capable of emitting a substantial amount of light inthe passband of color filter 671 without substantially emitting light inthe pass band of color filter 672 and is capable of emitting asubstantial amount of light in the passband of color filter 672 withoutsubstantially emitting light within the passband of color filter 671.Using a color display as the 2D light source it is possible to relax theresolution of the 2D light source needed to control the optocambackplane illustrated in FIG. 4 back to the resolution requirement ofFIG. 2.

FIG. 7 shows a side view of an optocam backplane 710 showing a crosssection of the backplane 2D output terminal array 730. The opticalswitches of the optocam backplane 710 are controlled by a 2D lightsource, e.g. a flat panel display 760. In FIG. 7, the pixel pitch of thebackplane 710 is substantially equal to the pixel pitch of the 2D lightsource 760 and the substrate thickness, d, of the backplane issufficiently small such that crosstalk due to dispersion of light fromthe light source pixels is not significant. In this scenario, the lightsource 760 can be directly coupled to the optocam backplane 710 withoutintervening optics.

FIG. 7 illustrates an embodiment wherein a flat panel display 760, e.g.,organic light emitting diode (OLED) display or liquid crystal display(LCD), is directly optically coupled to the back of a optocam backplane710. As long as the substrate thickness of the optocam backplane, d, ismuch smaller than the pixel pitch of the backplane optical switch array,this approach should be sufficient. Taking advantage of current trendsin thin transparent substrates developed in current display industry,this approach is may be useful. If the required array pitch is smallerthan the substrate thickness, appropriate relay optics 870, shown inFIG. 8 may be used. The relay optics 870 are shown disposed along asurface of the backplane 810 opposite from the output terminals 830. Forexample, the relay optics 870 may comprise a pinhole mask to blockdispersed light and/or a micro lens array, e.g., a selfoc lens array,configured to focus light from the display 860 onto the optical switchesof the optocam backplane 810.

FIG. 9 shows a configuration that uses a projector system including aprojector 961 used as the light generating device, a tilted mirror 963,and a scanning mechanism 962 configured to translate the tilted mirroralong one or more axes. The projector 961, mirror 963, and scanningapparatus 962 can provide the pixelated 2D light source for controllingthe optical switches of the optocam backplane 910 to provide a desiredpattern output at the output array 930 of the optocam backplane.Compared to the configuration shown in FIG. 7, for example, a projectorsystem usually requires bulkier optics. The projector system providesseveral useful features. For example, if an optocam backplane withsingle optical switch pixels as in FIG. 2 is used, optical zoom of theprojector can be used to generate potential map patterns that can beeasily scaled, independent of the pre-designed array pitch. The mirrorand the projector can also be engineered to scan in 1D or 2D in realtime such that a large pattern field can be provided.

As an alternative to the projector, mirror, and scanning apparatus ofFIG. 9, it is possible to use a digital light projector (DLP) system,which incorporates many pixel sized rotatable micro-mirrors with ascanning mechanism that tilts the mirrors toward or away from the lightbeam generated by the projector, thus turning the optical switches on oroff.

FIGS. 10 and 11 are graphs that illustrate the operation of an optocambackplane that has the pixel circuit and connection as shown in FIG. 2and the 2D optical source as shown in FIG. 9. The measurements wereperformed with an oscilloscope (TDS2014B) and a high impedance voltageprobe (Trek 800 high impedance Voltmeter). FIG. 10 shows the signaldetected by a probe hovering above a light square that is turned on 0.1s, in sync with the positive rising edge of V1. FIG. 11 shows a similarmeasurement but the probe is hovering above a light square that isturned on 0.1 seconds, in sync with the falling edge of negative V1cycle. Both FIGS. 10 and 11 show the pixels are charged to the designedvoltage rapidly and decay slowly (following the voltage of V1) when theoptical light source is turned off, which is what is expected for theoptocam backplane operation. The refresh rate of this measurement was 2seconds, however, for practical applications, a much higher refreshingrate can be used to minimize the rippling of voltage outputs.

Applications of the optocam backplane described above include highvoltage switching to control devices such as MEMs devices. High voltageswitching is usually not compatible with standard VLSI processes. Onetechnique for isolating high voltage from low voltage circuits involvesthe use of an optocoupler. However, as illustrated by FIG. 12, standardPIN photosensors are unsuitable for high voltage applications because oftheir high leakage current at high reverse bias voltage. FIG. 12 is agraph of dark and light IV characteristic of a standard PIN (i-a-Si:H)photosensor having an area of 1 mm² and a thickness of 1 μm. As shown inFIG. 12, the on/off ratio drops quickly for |V|>20V and drops to below10 after 50V.

Embodiments disclosed herein include thin film semiconductor opticalswitches that can be used in various applications, including the optocambackplane previously discussed. Suitable structures for the thin filmoptical switches described herein can be similar in some respects to thestructure of thin film transistors (TFTs). A thin film transistor (TFT)is a three terminal device made by depositing thin films (e.g. havingthicknesses in a range of about 1 nm to 10 μm) of active semiconductorlayers, dielectric layers, and metallic contacts over a non-conductingsupporting substrate.

However, the thin film optical switches according to the variousembodiments differ from thin film transistors in that they areconfigured to operate as two terminal devices, relying on lateralconduction in thin film semiconductors under illumination to build highvoltage photoconducting devices for high voltage optocouplers, targetingapplications that require ultralow leakage currents (about 1 pA at100V). Some embodiments described below involve thin film constructions,and some are based on a lateral p+/i/p+ structure.

The thin film optical switches described herein include one or morefield plates that shield the junction between the photosensitivematerial and at least one of the first and second laterally spacedelectrodes. The field plate can be electrically connected to theelectrode through vias or extension of the electrodes. The thin filmoptical switches disclosed herein provide a simple and effectivesolution that can be used in thin film optocoupler backplanes. Thedesigns disclosed rely on illumination to control the lateralconduction. These configurations obviate the need for any extra voltagesource to control transistor gates, which might lead to high voltagecross overs that can potentially create shorts.

The thin film optical switch configurations described herein havesimilar on/off ratios of greater than about 500, greater than about 750,or even greater than about 1000 over a voltage range from −100 to +100,at illumination levels of 500 cd/m². The thin film optical switches weretested using a microscope light that provided typical illuminationconditions, about 7×10¹³ photons/second. The illumination level is thesame for the measurements of FIGS. 12, 15, and 17. The dark stateleakage current of the optical switch may be less than about 1×10⁻¹²amperes at +/−100 V between the first and second electrodes.

FIGS. 13A and 13B show the cross section and lateral device structure,respectively, of the thin film optical switch which can be fabricatedusing a thin film compatible process. The optical switch includes aninsulating layer 1320, e.g., nitride, upon which a photo sensitive layer1310, e.g., a-Si:H, is disposed. First and second electrodes 1331, 1332(e.g., source and drain electrodes comprising a metal, metal alloy,transparent conductor, or doped n+ material) are offset laterally withrespect to the photo sensitive layer 1310. The electrodes 1331, 1332contact the photo sensitive layer 1310 at junction regions 1331 a, 1332a. An insulating layer, e.g., nitride layer 1350, may be disposed overthe photo sensitive layer 1310.

A field plate 1340 extends in the x and y directions along the photosensitive layer 1310. The field plate 1340 is electrically insulatedfrom the photo sensitive layer 1310 by the insulator layer 1320 and iselectrically connected to electrode 1332 at connection 1360. The fieldplate 1340 extends laterally in x and/or y directions by at least awidth that is larger than the separation along the z axis between thefield plate and the photo sensitive semiconductor 1310 in the junctionregion 1332 a in FIG. 13A. This separation between field plate 1340 andphoto sensitive semiconductor 1310 can be in the range of about 100 nmto about 1 μm. The extension beyond the junction region 1332 a in xand/or y directions can be greater than about 2 times of thickness(along the z axis) of the insulator 1320 in the junction region 1332 a.The thickness along the z axis of the photo sensitive semiconductorlayer 1310 may be in the range of about 50 nm to about 1 μm. Thethickness along the z axis of insulator 1320 in the junction region 1332a may be about 100 nm to about 1 μm. The thickness of field plate alongthe z axis may be between about 100 nm to a few microns.

The field plate 1340 having this configuration mitigates Poole Frenkelleakage current. The field plate 1340 is configured to shield thejunction region 1332 a from high electric fields that might result fromthe high voltage drop between the two electrodes 1331, 1332. The fieldplate 1340 may comprise a metal or may comprise a transparent conductivematerial such as indium tin oxide (ITO) to enhance optical response whenlight is shining from the bottom of the device as oriented in FIG. 13A.The illumination (LIGHT) in FIG. 13A is drawn shining from the top asoriented in FIG. 13A but in some configurations, the illumination can beshining from the bottom or can be shining from both top and bottom ofthe device. The electrodes 1331, 1332 may comprise a transparentconductive material in some embodiments.

FIGS. 13A and 13B illustrate a device with one field plate that isdesigned to provide high voltage shielding in one bias direction. FIG.14 shows the lateral structure of a device with two field plates 1441,1442. The device of FIG. 14 is designed to provide high voltageshielding in both bias directions. The field plates 1441, 1442 areconfigured to shield the junction regions 1431 a, 1432 a from highelectric fields that might result from the high voltage drop between thetwo electrodes 1431, 1432.

The device of FIG. 14 includes a photo sensitive layer 1410 withelectrodes 1431 and 1432 contacting the photo sensitive layer 1410 atjunctions 1431 a and 1432 a. Field plates 1441, 1442 extends in the xand y directions along the photo sensitive layer 1410. Field plates1441, 1442, are electrically insulated from the photo sensitive layer1410 by an insulator layer and are electrically connected to electrodes1431, 1432 at connections 1461, 1462. The field plates 1441, 1442 extendbeyond the respective junction regions 1431 a, 1432 a. For example, eachof the field plates 1441, 1442 may extend laterally in x and/or ydirections by at least a width that is larger than the separation of thefield plate 1441, 1442 and the photo sensitive semiconductor in thejunction region 1431 a, 1432 a in FIG. 14. The separation between fieldplate 1441, 1442 and photo sensitive semiconductor 1410 is typically inthe range of about 100 nm to 1 μm. The extension beyond the junctionregion in x and y direction is usually greater than about 2 times ofthickness of the insulator layer. The thickness of the photo sensitivesemiconductor layer 1410 is in the range of about 50 nm to about 1 μm.The thickness of insulator is typically about 100 nm to about 1 μm. Thethickness of field plate 1441, 1442 is typically between about 100 nm toa few microns.

FIG. 15 shows the dark and light IV characteristics and the on/off ratioof a device having the configuration of FIGS. 13A and 13B. The devicetested uses MoCr as the electrode metal, which blocks some light butdiffused light is sufficient to turn on the device.

FIGS. 16A and 16B show the cross section and lateral device structure,respectively, of an optical switch based on a p+/i/p+ structure thatincludes field plates integrated into the source and drain electrodes.Although a lateral p+/i/p+ structure is shown in this example, thoseskilled in the art will appreciate that other structures with laterallyspaced electrodes may be used, for example, in some embodiments, thedevice could have a lateral p+/n−/p or a lateral n+/p−/n+ structure. Thedevice includes a photo sensitive layer 1610, e.g., a-Si:H, disposed onan insulating layer 1620, e.g. a nitride layer. The p+/i/p+ layers arelaterally spaced apart. First and second electrodes 1631, 1632 (e.g.,source and drain electrodes) are spaced apart laterally with respect tothe photo sensitive layer 1610 and contact the photo sensitive layer1610 at first and second junction regions 1631 a, 1632 a, respectively.In various embodiments, the electrodes 1631, 1632 may comprise a metal,metal alloy, e.g., MoCr, a p+ doped material, or a transparent conductorsuch as ITO.

Field plates 1641, 1642 extend laterally beyond the junction regions1631 a, 1632 a, and are electrically connected to electrodes 1631, 1632,respectively. The field plates 1641, 1642 are electrically insulatedfrom the photo sensitive layer 1610 by insulator regions 1621 a,b, 1622a,b. The field plates 1641, 1642 may extend beyond the junction regions1631 a, 1632 a over one or more of the insulator regions for greaterthan about 2 times the thickness of the insulator layer 1621 a,b, 1622a,b between field plate and photo sensitive semiconductor. The insulatorlayer 1621 a,b, 1622 a,b may have a thickness, for example between about100 nm to 1 μm near the junction regions 1631 a, 1632 a. The thicknessof the photo sensitive semiconductor layer 1610 in the may be betweenabout 50 nm to 1 μm. The field plate 1641, 1642 may be about 100 nm to 1μm thick.

FIG. 17 shows the dark and light IV characteristics and on/off ratio ofa device having the structure of FIGS. 16A and 16B. Roughly three ordersof magnitude is observed through −100 to +100 V bias. The zero crossingof the dark IV characteristic was shifted to −25V because of therelatively high sweeping rate.

Optical switches disclosed herein are designed to use lateralphotoconductivity plus one or more field plates to shield thesemiconductor junction from high electric fields. The disclosedstructures provide optical switches compatible with high voltageapplications. These optical switches are compatible with large areaprocesses and can include light sensitive undoped semiconductors such asi-a-Si:H, for example. The two electrodes (e.g., source and drain) areoffset laterally with respect to the semiconductor layer. The lightsensitive semiconductor layer can be planar, or, in some embodiments,the light sensitive semiconductor layer can be conformally depositedover one or more non-planar sub-structures, such as a mesasub-structure.

The junction between the photo sensitive semiconductor layer and one orboth of the electrodes is covered by a field plate that is at the samepotential as the electrode, shielding the electrode to semiconductorjunction. In various embodiments, the control light feeds from the top,bottom or both the top and bottom of the optical switch.

The foregoing description of various embodiments has been presented forthe purposes of illustration and description and not limitation. Theembodiments disclosed are not intended to be exhaustive or to limit thepossible implementations to the embodiments disclosed. Manymodifications and variations are possible in light of the aboveteaching.

What is claimed is:
 1. A device comprising: a backplane, comprising:multiple output terminals arranged on an output surface of thebackplane; an optocoupler active matrix array, comprising: thin filmsolid state optical switches coupled respectively between an inputterminal of the backplane and the output terminals, the optical switchesand the output terminals arranged in an array; and storage capacitorscoupled respectively to the output terminals; and a pixelated lightsource configured to provide pixelated light that controls the opticalswitches.
 2. The device of claim 1, wherein the pixelated light sourcecomprises: at least one light generating device configured to provide alight beam; and at least one mirror; and a movement mechanism configuredto provide movement of the mirror along at least two dimensions.
 3. Thedevice of claim 1, wherein the pixelated light source comprises multiplelight generating devices, each of the multiple light generating devicesarranged to control at least one of the optical switches.
 4. The deviceof claim 1, wherein the pixelated light source comprises: at least onelight generating device; and a micro mirror array comprising multiplerotatable micro mirrors.
 5. The device of claim 1, wherein the pixelatedlight source comprises a flat panel display, wherein each pixel of theflat panel display corresponds to a pixel of the active matrix array. 6.The device of claim 5, wherein an array of optical devices is disposedbetween the flat panel display and the active matrix array.
 7. Thedevice of claim 6, wherein the array of optical devices comprises atleast one of a microlens array, a selfoc lens array, and a pinholearray.
 8. The device of claim 1, wherein: the optical switches arearranged in pixel groups, each pixel group including at least a firstoptical switch coupled to a first input and a second optical switchcoupled to a second input, the first and second optical switchesconnected to a common output terminal and capable of being individuallyactivated by the pixelated light source.
 9. The device of claim 1,wherein: the optical switches are arranged in pixel groups, each pixelgroup including at least a first optical switch coupled to a first inputand a second optical switch coupled to a second input, the first andsecond optical switches connected to a common output terminal; a firstoptical filter having a first passband color arranged between thepixelated light source and the first optical switch; a second opticalfilter having a second passband color arranged between the pixelatedlight source and the second optical switch; and, wherein the pixelatedlight source is configured to activate the first optical switch byemitting the first color and to activate the second optical switch byemitting the second color.
 10. A device comprising: a backplane,comprising: multiple output terminals arranged in an array on an outputsurface of the backplane; and an active matrix array, comprising: thinfilm solid state optical switches coupled respectively between at leastone input terminal of the backplane and the output terminals, eachoptical switch comprising: a layer of photo sensitive material thatextends laterally; first and second electrodes spaced apart laterallyfrom one another along the layer of photo sensitive material, the firstand second electrodes contacting the photo sensitive material at firstand second junctions, respectively; and at least one field plateelectrically insulated from the photo sensitive material and extendinglaterally along the layer of photo sensitive material and beyond thefirst and second junctions, wherein the at least one field plate iselectrically connected to the first electrode or the second electrode.11. The device of claim 10, further comprising storage capacitorscoupled to each of the output terminals.
 12. The device of claim 10,further comprising a voltage source coupled to the at least one inputterminal.
 13. The device of claim 12, wherein: the voltage sourceprovides a time varying input voltage at the input terminal: and theactive matrix array is configured to provide multiple voltage levels atthe outputs based on the time varying input voltage.
 14. The device ofclaim 12, wherein the optical switches are arranged in pixel groups,each pixel group including at least a first optical switch coupled to afirst input terminal and a second optical switch coupled to a secondinput terminal, the first and second optical switches connected to acommon output terminal; and the voltage source is configured to providea first input voltage, V_(i1), at a first input terminal and to providea second input voltage, V_(i2), at a second input terminal.
 15. Thedevice of claim 14, wherein active matrix array is configured to providemultiple voltage levels at the outputs, wherein the multiple voltagelevels are between the first and second input voltages.
 16. The deviceof claim 12, wherein: the at least one input terminal comprises a firstinput terminal and a second input terminal; and the voltage source isconfigured to provide a periodically changing voltage at the first inputterminal and to provide a constant voltage at the second input terminal.17. The device of claim 16, wherein the second input terminal is held at0V.
 18. The device of claim 10, wherein the optical switches arearranged in pixel groups, each pixel group arranged to convert a digitalinput signal to an analog output signal.
 19. The device of claim 10,wherein each optical switch in the active matrix array is configured tobe individually addressed by on/off control of a pixel of a pixelatedlight source.